Potential in Passaic Valley for snow, ice to jam up rivers, culverts

The Passaic River, shown here at the Glover Avenue bridge looking towards Woodland Park, was recently frozen from bank to bank. With recent severe snowfall, experts are concerned aboutpotential for flooding as a result of runoff and snow-ice clogs.

With 15 snowfalls under the Passaic Valley’s belt in just two months, and times of extreme cold, the specter of flooding along local rivers has been raised as a result of both runoff and "snow-ice dams" clogging the waterways.

Nicholas Agnoli, chairman of the Passaic Valley Regional Flood Control Board, and a flood control expert by trade, is concerned that "rain on snow" event could lead to flooding along the Passaic and Peckman Rivers in the Passaic Valley area, but the cold combined with last Thursday’s heavy snowfall brought to mind a similar problem.

"There is a potential not only for the snow to become runoff, there is also the potential for snow-ice dams as they’re called. Ice forms along the river. It jams up in bridges and it jams up on culverts, and that’s where you can get some high flows," he said, adding, "That can be very serious and very dangerous."

David Robinson, the New Jersey State Climatologist at Rutgers University said on Jan. 11 that up until a week ago he wasn’t concerned there was a threat of flooding. But that changed quickly.

"We got those two very wet storms last week and with those two storms we do have to be concerned about the water that’s locked up," he said.

"We’re primed for some potential problems," Robinson said. "Were there not some snowpack there, or not as rich a snow pack there, we wouldn’t have that added concern."

He said that as of that day, more than two inches of water was locked up in the snowpack in the Passaic River Basin. "If you have a rapid melt, it’s putting the equivalent of a significant rain storm in the rivers - and in a matter of a few days," Robinson said.

"A run of the mill rain storm with even half that pack puts two to two and a half inches of water into streams," he said adding that runoff is increased if the ground is frozen.

Robinson said the Passaic River Basin gets into a situation this time of the year and in early March when there is snow on the ground. "The hope is it is not accompanied by a major rain event and most of the time we dodge it," he said.

However, that hope doesn’t always come true. In 1982 built up snowpack lead to "some of the worst floods on record" and in 1994, he said, a very snowy winter was followed by flooding.

Although, sometimes, there’s snowpack and flooding, but the two are not related as was the case in 2011 before Hurricane Irene.

"In March of that year we had had a pretty hefty season of snow fall and a long duration of snow cover and we had got to late March and as I recall there was at least 3 inches of water locked up in the snowpack," he said.

However, Robinson added most of the snow melted over the course of a week to 10 days before the rainstorms arrived.

Little Falls Mayor Darlene Post was not as concerned about the potential for river flooding as the scientists, rather she was anticipating possibility of localized flooding on municipal roadways.

"We’re not anticipating a problem with the Peckman and Passaic at this juncture, but obviously we’re going to keep a very watchful eye on the rivers because we don’t want them to come over their banks," she said. "Holy snow. I don’t think I’ve every seen this much snow since I’ve been a little girl."

The township’s Department of Public Works (DPW) was addressing the possibility of localized roadway flooding last Friday morning as a result of the snowfall.

"Right now my DPW is out there clearing all the drains," Post said. "We do expect a meltdown."